This invention relates generally to electricity metering, and more particularly, to calibration of a microcomputer based electricity meter.
Some known electronic electricity meters for metering multi-phase services include a digital signal processor (DSP) and a microcomputer. The DSP processes the digital voltage and current signals to generate metering values, and then the microcomputer uses such metering values to generate additional values, e.g., demand and kVA. Data and commands are communicated between the DSP and the microcomputer.
For some metering installations, voltage and/or current being supplied to the load is too high for direct coupling of the meter to the power line. Therefore, voltage transformers and/or current transformers are utilized to step down the voltage and/or current. Stepping down the voltage and/or current, however, can adversely affect the accuracy of the measurement of energy consumed by the load.
In one aspect, an electronic electricity meter which comprises voltage sensors configured to generate measurements of voltage at voltage elements, current sensors configured to generate measurements of current through current elements, a microcomputer coupled to the current and voltage sensors and configured to control operation of the meter, and a memory coupled to the microcomputer and configured to store configuration and metering data, is provided. The memory further comprises calibration constants to compensate for instrument transformer ratio and phase angle errors, and the microcomputer is configured to use the calibration constants, when so instructed, to correct for instrument transformer ratios and phase angle errors.
In another aspect, a method for compensating for instrument transformer induced measurement errors in an electronic electricity meter is provided. The method comprises configuring the meter memory with calibration constants to compensate for instrument transformer induced ratio and phase angle errors, enabling the calibration constants via a software switch stored in the memory, and correcting measured metering quantities calculated by the microcomputer using the calibration constants.
In still another aspect, an electronic electricity meter is provided that is configured to store a set of calibration constants in a non-volatile memory of said meter for instrument transformer ratio and phase angle error compensation, store a software switch for enabling or disabling the instrument transformer ratio and phase angle compensation in the meter; and meter a plurality of electrical quantities of a power source. The meter having a microcomputer configured to selectively employ error compensation values, based on a value of the software switch and the calibration constants. The calibration constants are configured to compensate for errors by instrument transformers, and the calibration constants comprise at least one of a calculated instrument transformer gain coefficient for each voltage and current element in the meter, and an instrument transformer phase correction for each voltage and current element in the meter.
In yet another aspect, a processor for use in an electronic electricity meter is provided. The processor is configured to use calibration constants to compensate for instrument transformer ratio and phase angle errors, and the calibration constants comprise a determined instrument transformer gain coefficient for each voltage and current element in the meter and an instrument transformer phase correction for each voltage and current element in the meter.